Problem: Add.
Answer: There are many ways to solve this problem. Let's see two ways we can solve it. Place value table Let's line up the numbers by their decimal places. Tens Ones $.$ Tenths Hundredths $4$ ${2}$ $.$ ${2}$ ${5}$ $9$ $.$ ${0}$ ${0}$ Because ${9}$ is a whole number, we can add a decimal point and two $0$ 's behind to make the columns align. Now, let's add each place value column. Tens Ones $.$ Tenths Hundredths $\overset{1}{4}$ ${2}$ $.$ ${2}$ $5$ $+$ ${9}$ $.$ ${0}$ $0$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $5$ $1$ $.$ $2$ $5$ Decomposing the numbers We can group the whole numbers together and the decimals together. $\begin{aligned} &({42} + {9}) + {0.25}\\\\ &=51 + {0.25}\\\\ &=51.25 \end{aligned}$ $51.25 = 42.25 + 9$